Monday, June 26, 2017

Updating the CDC's IRAT (Influenza Risk Assessment Tool) Rankings

Credit NIAID

#12,575

Last September, before H7N9 reinvented itself (twice) in China, we looked at the CDC's ranking (seeCDC: IRAT Evaluation Of Novel Avian & Swine Flu Risks) of 11 novel flu subtypes/strains that circulate in non-human hosts and are believed to possess some degree of pandemic potential.

Not all novel flu viruses are created equally. Some show signs of being more likely to jump to humans than others, while some have shown more virulence in humans than others.

A mild flu, even if it spreads easily, isn't that much of a threat to public health. But a severe flu that spreads easily, is another matter entirely.

The CDC usestwo sets of criteria to evaluate novel viruses. One to estimate a virus's potential for sustained human-to-human transmission, and another to guage it'spotential for significant impact on public health.

Fast forward to June 2017, and the CDC has added two new viruses to their IRAT list (a second H7N9 [A/Hong Kong/125/2017] variant, and the recently arrived Canine H3N2) and has further refined their rankings.

Where there were 11 last September, there are now 13. It is worth nothing that of the 13 novel viruses on this list, 10 have been added in the past 6 years.

Below you'll find the latest rankings, with the new H7N9 virus nudging out the old version in both Emergence and Impact scores, putting both (A& B) far ahead of the pack.

Summaries on the two new entries, follow:

H3N2: [A/canine/Illinois/12191/2015]The H3N2 canine influenza virus is an avian flu virus that adapted to
infect dogs. This virus is different from human seasonal H3N2 viruses.
Canine influenza A H3N2 virus was first detected in dogs in South Korea
in 2007 and has since been reported in China and Thailand. It was first
detected in dogs in the United States in April 2015. H3N2 canine influenza has reportedly infected some cats as well as dogs. There have been no reports of human cases.

Summary: The average summary risk score for the
virus to achieve sustained human-to-human transmission was low risk
(less than 4). The average summary risk score for the virus to
significantly impact public health if it were to achieve sustained
human-to-human transmission was in the low risk range (less than 4).

The bigger concern comes from the recently emerged Yangtze River Delta lineage of H7N9 (we don't have enough data yet on the risks posed by the recently emerged HPAI version).

H7N9: [A/Hong Kong/125/2017]Low pathogenic avian influenza (LPAI) H7N9 viruses were first
reported from China in March 2013. These viruses were first scored using
the IRAT in March 2013 and again in April 2013, and then annually in
2014, 2015, and 2016 with no change in overall risk scores. Between
October 2016 and May 2017 evidence of two divergent lineages of these
viruses was detected – the Pearl River Delta lineage and the Yangtze
River Delta lineage. The IRAT was used to assess LPAI H7N9 [A/Hong
Kong/125/2017], a representative of the Yangtze River Delta viruses.

Summary: A risk assessment of H7N9 [A/Hong
Kong/125/2017] was conducted in May 2017. The overall IRAT risk
assessment score for this virus falls into the moderate-high risk
category and is similar to the scores for the previous H7N9 viruses. The
summary average risk score for the virus to achieve sustained
human-to-human transmission is in the moderate risk category (less than
7). The summary average risk score for the virus to significantly impact
public health if it were to achieve sustained human-to-human
transmission was in the moderate-high risk category (less than 8).

While IRAT can't tell us which virus will spark the next pandemic, or when that might happen, there are three major takeaways from these reports.

There are a lot of novel flu threats out there with at least some pandemic potential. IRAT currently evalluates 13, but that is by no means an exhaustive list.

New viruses appear to be emerging at an accelerated rate over the past decade.

Viral evolution requires that these viruses be re-evaluated from time to time, as nothing is static in the flu world. A virus that ranks relatively low today might be viewed as a serious contender a year or two from now.

All very good reasons why pandemic preparedess is getting renewed attention by the CDC, the WHO, and other government and NGO agencies around the world. You'll find some recent blogs on that below:

3 comments:

Hey Mike! According to CDC's summary of IRAT results, the H7N9 [A/Hong Kong/125/2017] entry was added in May 2017 and the H3N2 [A/canine/Illinois/12191/2015] entry was added (or last updated) in June 2016. Do you think this was a typo on their part or did they really add the latter strain to their list back in 2016?

They may very well have reviewed Canine H3N2 in June of 2016, but it wasn't on the chart when I blogged it in September. It was, however, on the list when I revisted the IRAT system on March 1st of this year.